The plan

Avoid any change that impacts backward compatibility. The intent is to add new functionality for those who need it, not to change the most common use case of a single database connection.

Add a new settings variable, OTHER_DATABASES. OTHER_DATABASES is a dict of named database connection parameter sets. In each set, the keys are the same as the standard database connection settings variables. Each set of settings may also define a list of models that will use that connection by default. Each item in the MODELS list may an app label (in which case it applies to all models with that app label) or app_label.Model, in which case it applies only to that specific model.

Add db attribute to Managers. This allows access to the connection that a model should use, as determined by settings. It may also be changed on the fly to use a different connection for a particular query or set of queries. When assigning to Manager.db, assign a django.db.ConnectionInfo; the easiest way to get one is from the django.db.connections dict.

Allow transaction decorators, etc to take optional connections argument. Without that argument, transactions will apply across all connections already in use.

Move generation of schema manipulating sql (CREATE TABLE, etc) from django.core.management into django.db.backends.ansi.sql. Schema statements are build with a SchemaBuilder instance; each backend gets an instance in its creation module as creation.builder.

Add methods to Manager to support per-model installation. This will enable each model to be installed using the connection that it specifies. It causes some complications, mainly in determining the correct order in which to install. My current solution is to depend on the developer already having figure that out by defining her models in a sensible order; and, when that fails, punting any unresolved constraints to the end of the syncdb or install process. The manager methods will delegate to each model's backend to do the sql creation.